Anomalies in the surface impedance penetration depth in ferromagnetic superconductors

Abstract We have investigated the surface impedance penetration depth, Λ, of ErRh 4 B 4 and Er 0.5 Ho 0.5 Rh 4 B 4 both experimentally and theoretically. For ErRh 4 B 4 , owing to the critical spin fluctuations just above T s ( > T c 2 ), the critical temperature at which surface ferromagnetism appears, Λ −1 decreases smoothly as T decreases toward T s . For Er 0.5 Ho 0.5 Rh 4 B 4 , the decrease in Λ −1 owing to spin fluctuations for T ⪆ T c2 is very small, and Λ −1 decreases abruptly at T c2 . Theoretical values of Λ −1 are in good agreement with the data.